As power storage devices used in mobile phones, portable terminal devices such as notebook computers, video cameras, satellites, electric vehicles, or the like, there are known, for example, lithium-ion batteries that can be made ultra-thin and small. In such a power storage device, contents such as a positive electrode material, a negative electrode material, a separator, an electrolytic solution, and the like are accommodated in a package, which is made by molding a packaging material for a power storage device (hereinafter may simply be referred to as a “packaging material”) into a predetermined shape. As the package, there has conventionally been used a metal can-type package made by press-molding a metal plate or the like. In recent years, because of a high degree of freedom in shape and ease of weight reduction, there has widely been used a laminate film-type package made by cold-molding a laminate film including a metal foil such as an aluminum foil (e.g., a laminated configuration composed of base layer/first adhesive layer/metal foil layer/second adhesive layer/sealant layer).
A power storage device that uses a laminate film as a packaging material is manufactured by deep-drawing a laminate film by cold-molding to form a recess, housing the device contents in the recess, and thermally sealing the perimeter portion. In the power storage device, a larger depth of the recess can achieve a larger capacity for accommodating the contents and a higher energy density. Accordingly, a polyamide film, which has good moldability and is likely to cause cracks or pinholes if the recess has a large depth is preferably used for the base layer of a packaging material (e.g., PTLs 1 and 2). However, the polyamide film fails to have sufficient resistance to electrolytic solutions. Accordingly, in the case where a plurality of power storage devices are stacked and used, for example, if one of the storage devices is broken and an electrolytic solution leaks therefrom, the electrolytic solution may adhere to the packaging material of other power storage devices located around the broken one. In this case, the base layer may be dissolved due to the electrolytic solution, causing corrosion of the metal foil layer inside the packaging material. Moreover, the polyamide film fails to have sufficient scratch resistance, and hence may suffer a scratch on a surface of the base layer when handled, and impair the aesthetic quality, durability, and the like of the packaging material.
On the other hand, PTL 1 shows that, for the purpose of further improving moldability of the packaging material, a matte varnish layer is formed on an outer surface of the base layer. The matte varnish layer is formed of an olefin or alkyd synthetic resin such as a cellulose resin, a vinyl chloride-vinyl acetate resin, a modified polyolefin resin, a rubber, an acrylic resin, a urethane resin or the like, and a matting agent such as of silica, a kaolin or the like. However, being provided with the matte varnish layer, it is difficult to sufficiently suppress degradation of the base layer caused by the electrolytic solution, and impart sufficient scratch resistance.
Packaging materials that have commonly been used for such lithium-ion batteries include nylon for the base layers. To impart resistance to electrolytic solutions or aesthetic quality to the base layers, there is also a proposal that a base protective layer should be provided on an outer side of the base layer.